A study of the coupled dynamics of asymmetric absorbing clusters in a photophoretic trap

TL;DR

This study investigates the complex rotational and oscillatory behaviors of asymmetric absorbing carbon clusters in a photophoretic trap, revealing how trap stiffness and cluster properties influence their dynamics, with implications for designing micromachines.

Contribution

It provides new insights into the coupled rotational and oscillatory dynamics of asymmetric clusters under photophoretic forces, highlighting the dependence on trap stiffness and cluster morphology.

Findings

Clusters exhibit rotation coupled with axial oscillation at high laser powers.

Rotation frequencies depend on trap stiffness, not laser power.

Clusters cease rotation below a certain laser power and show thermal fluctuations.

Abstract

We report a study on the dynamics of absorbing asymmetric carbon clusters trapped by a loosely focused Gaussian beam using photophoretic force. At high laser powers, all the trapped clusters display rotation coupled with oscillation along the axial direction, with a majority spinning about a body fixed axis, while the rest display dual spin as well as orbital motion about a fixed point in space. The spinning and orbiting frequency is inversely proportional to the amplitude of the axial oscillation - with one growing at the expense of the other. Further, the frequencies of these rotations are not proportional to the laser power, but to the trap stiffnesses inferred from the corresponding natural frequencies. The clusters also stop rotating below a certain laser power, and execute random thermal fluctuations. Our work suggests that the dynamics of clusters trapped with photophoretic force are largely dependent on the cluster size and morphology, which could, in principle, be tuned to obtain various motional responses, and help in the design of rotating micromachines in air.